With rapid development of mobile Internet services, a characteristic of uplink-downlink asymmetry for a mobile communications service is becoming obvious. For a high-bandwidth service such as an online video, a downlink traffic volume is far greater than an uplink traffic volume. Therefore, a mobile communications network assumes a contradictory characteristic of “downlink resources being scanty and uplink resources being more than needed”. Configuration of asymmetry between uplink and downlink timeslot resources can be implemented in a time division duplexing (TDD) manner, and the contradiction brought by asymmetry between the uplink and the downlink of a service can be reduced to an extent. However, limitations of a TDD system in aspects such as coverage and high-speed moving, and hysteresis quality of the TDD system in actual industrialization and internationalization processes cause a standardization organization such as the 3GPP to begin to emphasize how to implement, on the basis of frequency division dual (FDD), a flexible configuration of uplink and downlink resources.
In the 67th RAN plenum held in March in 2015, companies such as LG, China Telecom, Huawei, and Hisilicon jointly put forward a new project proposal of flexible duplex. This proposal claims that, flexible allocation of the uplink and downlink resources may be implemented by transmitting downlink data in some sub-frames on an uplink carrier of the FDD. FIG. 1 shows a solution of flexible allocation of frequency domain resources. By means of a method similar to carrier aggregation (CA), control-and-feedback-related information is transmitted by using a primary carrier, that is, a Primary Cell (Pcell), wherein the information is information such as physical uplink control channel (PUCCH) information (which comprises, for example, Acknowledgment/Negative Acknowledgement (ACK/NACK), a channel quality indicator (CQI), a precoding matrix indicator (PMI), and a rank indication (RI)) of all carriers. For example, a carrier 1 may be configured as a Pcell, and then control-and-feedback-related information of carriers 1/2/3 is transmitted by using an uplink carrier of the carrier 1. However, such a configuration method causes a load problem of the control-and-feedback-related information on the uplink carrier of the Pcell to be more serious. The reason for this is that: actually resources of five carriers (a downlink carrier 1, a downlink carrier 2, an uplink carrier 2, an downlink carrier 3, and an uplink carrier 3 that are shown in FIG. 1) are allocated for downlink transmission, and therefore the uplink carrier of the Pcell needs to bear feedback messages that are from the five carriers; second, only an uplink carrier that has a complete uplink sub-frame can be configured as the Pcell, and all user equipments can uses only the uplink carrier of the carrier 1 as an uplink Pcell, and therefore control-and-feedback-related information of all user equipments of an entire cell are borne by the same uplink carrier. In summary, according to a conventional Pcell configuration method, in an FDD flexible duplex system, an uplink carrier configured as a Pcell bear control-and-feedback-related information corresponding to all downlink sub-frames of all user equipments, which causes corresponding uplink feedback overheads to be extremely high.